Question

x(x-1)-(x平方-y)=-2,则x平方+y平方-2xy的值为

Answer 1

x(x-1) - (x² - y) = -2

x² - x - x² + y = -2

-x +y = -2

x - y = 2

所以 x² + y² - 2xy = (x-y)² = 2² = 4